Ancient DNA reveals diverse community in 'Lost City of the Incas'

Who lived at Machu Picchu at its height? A new study, published today in Science Advances, used ancient DNA to find out for the first time where workers buried more than 500 years ago came from within the lost Inca Empire.

Researchers, including Jason Nesbitt, associate professor of archaeology at Tulane University School of Liberal Arts, performed genetic testing on individuals buried at Machu Picchu in order to learn more about the people who lived and worked there.

Machu Picchu is a UNESCO World Heritage Site located in the Cusco region of Peru. It is one of the most well-known archaeological sites in the world and attracts hundreds of thousands of visitors every year. It was once part of a royal estate of the Inca Empire.

Like other royal estates, Machu Picchu was home not only to royalty and other elite members of Inca society, but also to attendants and workers, many of whom lived in the estate year-round. These residents did not necessarily come from the local area, though it is only in this study that researchers have been able to confirm, with DNA evidence, the diversity of their backgrounds. "It's telling us, not about elites and royalty, but lower status people," Nesbitt said. "These were burials of the retainer population."

This DNA analysis works in much the same way that modern genetic ancestry kits work. The researchers compared the DNA of 34 individuals buried at Machu Picchu to that of individuals from other places around the Inca Empire as well as some modern genomes from South America to see how closely related they might be.

The results of the DNA analysis showed that the individuals had come from throughout the Inca Empire, some as far away as Amazonia. Few of them had shared DNA with each other, showing that they had been brought to Machu Picchu as individuals rather than as part of a family or community group.

"Now, of course, genetics doesn't translate into ethnicity or anything like that," said Nesbitt of the results, "but that shows that they have distinct origins within different parts of the Inca Empire."

"The study does really reinforce a lot of other types of research that have been done at Machu Picchu and other Inca sites," Nesbitt said. The DNA analysis supports historical documentation and archaeological studies of the artifacts found associated with the burials.

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Machu Picchu: Ancient Incan sanctuary intentionally built on faults

Machu Picchu, Peru

The ancient Incan sanctuary of Machu Picchu is considered one of humanity's greatest architectural achievements. Built in a remote Andean setting atop a narrow ridge high above a precipitous river canyon, the site is renowned for its perfect integration with the spectacular landscape. But the sanctuary's location has long puzzled scientists: Why did the Incas build their masterpiece in such an inaccessible place? Research suggests the answer may be related to the geological faults that lie beneath the site.

On Monday, 23 Sept. 2019, at the GSA Annual meeting in Phoenix, Rualdo Menegat, a geologist at Brazil's Federal University of Rio Grande do Sul, will present the results of a detailed geoarchaeological analysis that suggests the Incas intentionally built Machu Picchu -- as well as some of their cities -- in locations where tectonic faults meet. "Machu Pichu's location is not a coincidence," says Menegat. "It would be impossible to build such a site in the high mountains if the substrate was not fractured."

Using a combination of satellite imagery and field measurements, Menegat mapped a dense web of intersecting fractures and faults beneath the UNESCO World Heritage Site. His analysis indicates these features vary widely in scale, from tiny fractures visible in individual stones to major, 175-kilometer-long lineaments that control the orientation of some of the region's river valleys.

Menegat found that these faults and fractures occur in several sets, some of which correspond to the major fault zones responsible for uplifting the Central Andes Mountains during the past eight million years. Because some of these faults are oriented northeast-southwest and others trend northwest-southeast, they collectively create an "X" shape where they intersect beneath Machu Picchu.

Menegat's mapping suggests that the sanctuary's urban sectors and the surrounding agricultural fields, as well as individual buildings and stairs, are all oriented along the trends of these major faults. "The layout clearly reflects the fracture matrix underlying the site," says Menegat. Other ancient Incan cities, including Ollantaytambo, Pisac, and Cusco, are also located at the intersection of faults, says Menegat. "Each is precisely the expression of the main directions of the site's geological faults."

Menegat's results indicate the underlying fault-and-fracture network is as integral to Machu Picchu's construction as its legendary stonework. This mortar-free masonry features stones so perfectly fitted together that it's impossible to slide a credit card between them. As master stoneworkers, the Incas took advantage of the abundant building materials in the fault zone, says Menegat. "The intense fracturing there predisposed the rocks to breaking along these same planes of weakness, which greatly reduced the energy needed to carve them."

In addition to helping shape individual stones, the fault network at Machu Picchu likely offered the Incas other advantages, according to Menegat. Chief among these was a ready source of water. "The area's tectonic faults channeled meltwater and rainwater straight to the site," he says. Construction of the sanctuary in such a high perch also had the benefit of isolating the site from avalanches and landslides, all-too-common hazards in this alpine environment, Menegat explains.

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